In the photocopying art, a two-component diazotype light sensitive material or copy sheet, which has first been exposed to a light image, is developed to produce thereon an azo-dye image by bringing the copy sheet into contact with a humidified atmosphere of ammonia vapor or gas. The gaseous ammonia is produced by heating an ammonium hydroxide solution such as 26.degree. Baume ammonia or by the use of anhydrous ammonia gas.
The construction of known copying equipment for developing copy sheets of this type involves the use of a gas chamber in which the ammonia vapor is generated directly from a tank containing aqueous ammonia, or the ammonia vapor is piped in from tanks of anhydrous ammonia which is admixed with water vapor generated within the gas chamber. The gas producing instrumentalities usually call for circulatory pumping equipment which continually supplies fresh aqueous ammonia and/or anhydrous gas into the chamber maintaining the chamber in a state of readiness to receive the copy sheets.
Photocopying machines relying on the gas developing process as a means for producing copies are desirable because the process is dry, obviating the need for bringing liquid materials into direct contact with the copy sheet for development. Also, such machines produce images of high density and are capable of developing copies at a rapid rate. However, while such developing apparatuses and systems have been generally satisfactory there are certain shortcomings associated with the devices. In this regard, the prior art devices do not provide for consistent uniform control of the moisture content to which the copy sheet to be developed is exposed, for uniform control of the distribution of the gaseous ammonia within the developer tank and for utilization of substantially all of the ammonia gas contained in the aqueous ammonia.
One such prior art device is disclosed, for example, in U.S. Pat. No. 2,630,744 and comprises a developing chamber including an open trough sloped downwardly towards a discharge opening and an evaporator pipe positioned above the trough provided with perforations for expelling ammonia gas from the pipe. Aqueous ammonia is supplied to one end of the pipe. The pipe is formed such that its intermediate portion is lower than the ends of the pipe whereby a pool of aqueous ammonia is maintained therein.
The pool of aqueous ammonia is maintained in the pipe for evaporation of the ammonia gas from the aqueous ammonia, and the residue of water and a trace of ammonia gas are discharged from the other end of the pipe to the high end of the open trough. The water is evaporated as it flows downwardly in the trough to provide the moisture requirements in the developing chamber and the excess water exits through the discharge opening.
The evaporation of the aqueous ammonia in the pipe and the vaporization of the water in the trough are effected by a heating element which is formed to heat both the pipe and the residue in the trough. The aqueous ammonia in the pipe is heated to drive off ammonia gas which exits through the perforations in the pipe, and the residue is separately heated to drive off water vapor to satisfy the moisture requirements in the developing chamber.
Additionally, the prior art device includes a wick for feeding the aqueous ammonia through the pipe by capillary action and for providing a large surface for effecting evaporation of the aqueous ammonia while the residue thereof is discharged into the trough.
Because the device of the prior art evaporates the aqueous ammonia in and discharges both the ammonia gas and the residue from a common pipe, rather than at separate sources as in the present invention, the device is unable to provide control of the moisture quantity and uniform controlled distribution of the ammonia gas. Thus, because the aqueous ammonia cannot be heated uniformily throughout the length of the pipe, the amount of gaseous ammonia evaporated from the aqueous ammonia also varies from one section to another section of the pipe. Accordingly, the amount of gaseous ammonia expelled from the pipe also varies from section to section, thereby precluding uniform and controlled distribution of the gaseous ammonia from the pipe to the developing chamber.
Further, because the prior art device is unable to provide the proper moisture content solely by evaporating the aqueous ammonia, it necessitates the additional heating of the residue in the trough to vaporize the water therein in an attempt to satisfy the moisture requirements. However, the open trough is neither conducive to providing a controlled moisture quantity nor to uniform distribution of the moisture with the gaseous ammonia discharged from the pipe.
In the present invention, control of the moisture quantity, controlled distribution of the gaseous ammonia and almost complete utilization of the ammonia gas are attained as a result of confining aqueous ammonia flow and separation thereof into ammonia gas and residue waste to a first path, and confining flow and distribution of ammonia gas only to a second path.
Proper moisture content is obtained solely by evaporating the aqueous ammonia by heating the first path only to separate the aqueous ammonia into ammonia gas and residue waste. The residue waste is discharged from one end of the first path and the ammonia gas travels in the opposite direction and is directed from the other end of the first path to the second path. The ammonia gas entering the second path provides a consistently uniform moisture content, and the ammonia gas is discharged from the second path in a controlled manner such that no further vaporization of the residue or water is required to satisfy the moisture requirements within the developer tank.